Javascript DRY Pattern - function

Question

New to OO, I am making a game and I have this as my initialState :

let initialState = {
  grid : null,
  player : {
    coordinates : null,
    health : 100 ,
    weapon : "Stick",
    expLevel : 1
  },
  enemies : [],
  weapons : [],
  items : []
}

when DOM is loaded, I am able to initialize weapons and items corretly. However, both of these properties share the exact functionality except the object literal that is initialized :

initialState.weapons = placeWeapons(3);
initialState.items = placeItems(2);

where placeWeapons

function placeWeapons(numberofWeapons){
  let weapons = [];
  let availableSpots = [];
  let placementWeapons = []; //list of coordinates that will place weapons
  let grid = initialState.grid;

  //collect whats available of coords that are not taken in initialState.occupiedCoordinates
  grid.forEach( (row, rowIndex) => (
    row.forEach( (cell, colIndex) => {
      if (cell === 1){
        availableSpots.push([rowIndex,colIndex])
      }
    })
  ))

  //lets place the weapons. When placed, it will update initialState.occupiedCoordinates
  while( placementWeapons.length < numberofWeapons ){
    let randCoords = availableSpots[Math.floor(Math.random() * availableSpots.length)];
    if (grid[randCoords[0]][randCoords[1]] === 1){
      placementWeapons.push(randCoords);
      grid[randCoords[0]][randCoords[1]] = 0
    }
  }
  placementWeapons.forEach( coord => {
    let weapon = {
      name : "Weapon Name",
      coords : coord,
      damage : 3
    }
    weapons.push(weapon)
  })
  return weapons;
}

placeItems

function placeItems(numberofItems){
  let items = [];
  let availableSpots = [];
  let placementItems = []; //list of coordinates that will place items
  let grid = initialState.grid;

  //collect whats available of coords that are not taken in initialState.occupiedCoordinates
  grid.forEach( (row, rowIndex) => (
    row.forEach( (cell, colIndex) => {
      if (cell === 1){
        availableSpots.push([rowIndex,colIndex])
      }
    })
  ))

  //lets place the items. When placed, it will update initialState.occupiedCoordinates
  while( placementItems.length < numberofItems ){
    let randCoords = availableSpots[Math.floor(Math.random() * availableSpots.length)];
    if (grid[randCoords[0]][randCoords[1]] === 1){
      placementItems.push(randCoords);
      grid[randCoords[0]][randCoords[1]] = 0
    }
  }
  placementItems.forEach( coord => {
    let item = {
      name : "Item Name",
      coords : coord,
      health : 3
    }
    items.push(item)
  })
  return items;
}

How can I DRY this pattern?

Make it easier by writing a function that returns an array of possible placements. — Bergi
– Bergi, Commented Nov 2, 2016 at 2:56

slebetman · Accepted Answer · 2016-11-02 03:18:16Z

The only significant difference I see is the thing being placed. So the logical thing to do is extract that and pass it in as an argument:

// WARNING: Untested code:
function placeThings(thing, numberofThings){
  let things = [];
  let availableSpots = [];
  let placementItems = []; //list of coordinates that will place things
  let grid = initialState.grid;

  //collect whats available of coords that are not taken in initialState.occupiedCoordinates
  grid.forEach( (row, rowIndex) => (
    row.forEach( (cell, colIndex) => {
      if (cell === 1){
        availableSpots.push([rowIndex,colIndex])
      }
    })
  ))

  //lets place the items. When placed, it will update initialState.occupiedCoordinates
  while( placementItems.length < numberofThings ){
    let randCoords = availableSpots[Math.floor(Math.random() * availableSpots.length)];
    if (grid[randCoords[0]][randCoords[1]] === 1){
      placementItems.push(randCoords);
      grid[randCoords[0]][randCoords[1]] = 0
    }
  }
  placementItems.forEach( coord => {
    things.push(Object.create(thing))
  })
  return things;
}

Now you can do:

// Weapons:
placeThings({
  name : "Weapon Name",
  coords : coord,
  damage : 3
},50);

// Items:
placeThings({
  name : "Item Name",
  coords : coord,
  health : 3
},100);

If you want to make the things being placed random you can just pass a function instead of an object:

// WARNING: Untested code:
function placeThings(thingGenerator, numberofThings){
  let things = [];

  /*
   * bla bla..
   */

  placementItems.forEach( coord => {
    things.push(thingGenerator())
  })
  return things;
}

So you'd do something like:

placeThings(makeWeapon, 50);
placeThings(makeItem, 100);

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